Craftsman 919.165370 Owner's Manual page 13

Air Compressor Pump (not shown):
Compresses air into the air tank.
Working air is not available until the
compressor has raised the air tank
pressure above that required at the
air outlet.
Check Valve: When the air
compressor is operating, the check
valve is "open", allowing compressed
air to enter the air tank. When the
air compressor reaches "cut-out"
pressure, the check valve "closes",
allowing air pressure to remain inside
the air tank.
13- ENG A08595